Traditional spiders contain a plurality of slips circumferentially surrounding the exterior of the pipe and are housed by what is commonly referred to as a "bowl". The bowl is regarded to be surfaces on the inner bore of the spider. Generally, the apparatus is engaged by placing it around a given section of pipe in the tubing string. The radial interior of the slips typically carry or form hard metal teeth for engaging the pipe. The exterior surface of the slips and the interior surface of the bowl usually have opposing engaging surfaces which are inclined and downwardly converging. In certain embodiments, the slips function like a wedge between the pipe surface and the bowl surface to provide a relationship between vertical and lateral slip movement. The greater the downward load imposed upon the slips by the pipe, the greater is the lateral force applied between slip and pipe at the pipe gripping surfaces. Further, when the pipe string is lifted by the rig hook and the pipe load is no longer on the slips, the slips are automatically free of surface loading forces and can readily move to clear the pipe surface. This process is referred to in the industry as a "self energizing" method of engaging the pipe for supporting the weight of the pipe string being suspended from the spider. The spider is supported by rig related structure.
During traditional well bore related operations, a spider which houses the slips, is located above the rotary table and is used for supporting the pipe suspended in the well by the bowl. In typical operations the spider remains stationary and the pipe is moved up or down by pipe gripping means supported by the rig hook. The hoisting apparatus engages the pipe to support the string before the slips in the spider are disengaged from the pipe. To reposition the hoisting apparatus relative to the pipe, the spider supported slips are again engaged before the hoisting apparatus releases the pipe load. Switching the load carrying function takes place each time a joint of pipe is added to, or removed from, the string. Time is saved in the slip management activity by using power actuating contrivances to lift and lower the slips relative to the bowl. The nature of pipe gripping contrivances in both the spider and the hoisting apparatus, for obvious safety reasons, are such that the slips cannot be released from the pipe until the pipe load is supported by another means.
The rotary table traditionally has a non-circular torque transmitting recess in the top just below the rig floor level with a round bore proceeding downward to accept a vertical pipe string. The drilling Kelly drive bushing normally fits in the rotary bore, engaging the recess, with all rotating parts generally flush with the rig floor. The rotary drilling art evolved with that configuration for obvious safety reasons. During the early years when wells were shallow, casing and tubing operations were simple and reasonably brief. The apparatus used to safely support casing or tubing strings were added atop the rotary drive and protruded upward several feet into the traditional rig crew work area. The wells are now deeper and the pipe string related activity has become more demanding and the spider related machinery is now mostly powered and bulky. The typical pipe string support spiders cannot be lowered into the rotary bore to be flush with the rig floor until the rotary drives are increased in size, or the spider assembly is consolidated and reduced in size, or both.
In the early years when pipe strings weighed less, some misalignment with the slips was not a matter of great concern. Additionally, the usually small well bore began just below the rig floor and little misalignment could occur. Today, many feet of pipe may be suspended in a large conductor pipe below the rotary and misalignment can be greater. Also, the very large pipe loads suspended by the slips invite damage to pipe surfaces. When well bore activities take place from floating assets the alignment of the rotary table axis may vary from the vertical even if the pipe has no such misalignment. The alignment matter requires attention.
The pipe manipulation processes described above have remained constant over many years but the pipe supporting machinery used frequently is improved. For example, U.S. Pat. No. 4,381,584 to Coyle, Sr. And U.S. Pat. No. 4,354,706 to Coyle, Sr. Provide for a dual string spider and/or elevator which cannot angularly adjust. The Coyle, Sr. Patents disclose slips which function to grip and support the pipe but they do not provide for angular adjustment in any plane or direction to accommodate angular change in the pipe centerline relative to the generally vertical centerline of the bowl. Misalignment between the pipe centerline and the general centerline of the gripping surfaces of the slips can damage the outer surface of the pipe string.
U.S. Pat. No. 5,335,756 to Penisson is restricted in it's radial movement of the slips and related gripping elements. Penisson does not provide a gripping assembly that can angularly align itself as an entire unit. In response to tilt of the pipe axis under load each gripping surface has to apply the unbalanced forces necessary to force alignment of independent assemblies. This may cause independent slip movement relative to pipe that can be especially destructive to pipe surfaces.
It is therefore an object of this invention to provide slip assemblies and related supporting surfaces that can move angularly as a unit relative to the bowl when supporting a string of pipe to allow the pipe axis to tilt about both horizontal axes relative to the generally vertical axis of the spider.
It is another object of this invention to provide apparatus to permit tilt of the pipe string axis relative to the supporting spider axis with machine components that will reside within the rotary table with the top of the spider generally flush with the rig floor.
It is yet another object of this invention to provide powered slip manipulating contrivances, for the spider, that reside in the bore of the rotary table when the slips are gripping pipe.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached claims and appended drawings.